Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 011113
Area Forecast Discussion
National Weather Service Lincoln IL
613 AM CDT Fri Aug 1 2014
ISSUED 317 AM CDT Fri Aug 1 2014
Same pattern over the CONUS, with a broad trof over the eastern
half and ridging in the west, leaving northwesterly flow across
the Plains and into the Midwest. Cooler air remains over the
region. A couple waves moving around the trof and enhancing the
chance for showers and thunderstorms today...and possibly into
tomorrow. However, a wave expected to move into the west coast
will help to push the broad eastern trof out of the way, leaving
next week in far more progressive westerly flow with several waves
and boundaries creating a far messier picture for next week, with
better chances for rain, particularly into Thursday. Allblend
not really handling definitive features well into the longer
range. Short term, models seem more in agreement for today, though
the nature of the scattered convection remains. Tomorrow, the
models have flip flopped a bit with regards to coverage of the
potential showers and thunderstorms.
SHORT TERM...Today and tomorrow...
Not much of a shift in the forecast overall, though SPC has
dropped the see text for Central Illinois. Forecast soundings
still showing lower freezing levels and decent lapse rates in the
mid levels...with less support aloft. Weak wind profiles remain.
Trof of cold air aloft will keep the instability in the profiles
and the short wave should help to kick off some showers and
thunder for today, particularly with the timing of the wave
matching with best daytime heating. With any rainfall for today,
big issue for tomorrow will be the potential for early morning
fog. Will keep from putting it in the forecast as the rainfall
will need to materialize first and xover temps this afternoon will
be very telling. Tomorrow had prev showed similar situation with
respect to thunderstorms, but with this 00z run, the trof is moving out to the
east and the instability is starting to lag a bit. Keeping the
slight chances in the far east, closer to the upper trof.
LONG TERM...Sunday through Thursday...
Sunday dries out in the forecast and high pressure dominating
remains of weekend as the sfc ridge axis moves into the region.
Winds remain light and variable and dry forecast as the upper trof
finally starts to progress across into the NE. Chances for more
significant weather starting to return Tues/Wed as a more active
and progressive flow sets up across the country. With the return
to a less amplified flow... a weak baroclinic zone sets up across
the nrn Plains and into the Midwest, parallel to the flow aloft.
Several waves moving quickly out of the west and along the
boundary start producing precip and begin a wet trend in the
remains of the forecast, depending on where the
boundary/shortwaves set up.
ISSUED 605 AM CDT Fri Aug 1 2014
A brief period of MVFR or lower vsbys in ground fog until 13z, the
VFR conditions are expected into this evening. Convection chances
and coverage today the main forecast concern as a weak upper level
disturbance tracks across the region. Convection occurring early
this morning looks to be tracking north of the TAF sites but will
have to watch PIA as some showers developing over west central IL
just recently may affect that airport over the next several hours
if it can hold together. Forecast soundings showing cumulus developing
by late morning with a bit better coverage of the cu field with cig
bases around 4500-5000 feet. Coverage of storms will be too limited
to include anything but VCTS with any thunderstorms expected to
dissipate with loss of daytime heating early this evening. If the
rainfall today is large in areal coverage than what is currently
expected, then the fog potential will increase across the forecast
area. For now, will bring vsbys down to around 5 miles late in the
evening, at least to get a trend started. Surface winds will not
be a factor today, although any thunderstorm close to a TAF site
will produce some gusty winds along with a wind shift along the
outflow boundary. The prevailing direction today should be out
of the southwest, and then nearly calm again tonight.